1. Field of the Invention
The present invention relates to an image forming apparatus, such as a digital copying machine, which has a hard disk drive for storing print jobs in the form of job files and which prints job files, one by one. The present invention also relates to a method of forming images in which job files stored in a hard disk drive are printed one by one.
2. Description of Related Art
A digital copying machine has a hard disk drive for storing print jobs in the form of job files and which prints the job files, one by one. Each print job consists of image data and print data, and is processed in the form of a file called a "job file". The job file consists of job data and page data.
To print each page recorded in a job file, the printing module incorporated in a conventional digital copying machine needs to refer to both the job data and the page data one by one, to determine which printing sequence would be the most appropriate. Assume the job data shows that data should be printed on both sides of a paper sheet, and also shows that the first, second and third pages should be printed on an A4-size sheet, an A3-size sheet and an A3-size sheet, respectively. In this case, the printing module must recognize the sheet size (i.e., A3) for the second page before it prints the first page on an A4-size sheet. Then the printing module must invalidate the double-side print mode, feed an A4-size sheet to the printing position, and print the first page on one side of the A4-size sheet. Further, the printing module must recognize the sheet size (i.e., A3) for the third page before it prints the second page on an A3-size sheet. Since the second and third pages are the same sheet size (i.e., A3 size), the printing modules feeds an A3-size sheet to the printing position and prints the second and third pages respectively on the two sides of the A3-size sheet.
Namely, before printing any page of data, the printing module needs to recognize the size of the paper sheet on which the next page of data should be printed. The operating program of the printing module is inevitably complex. The module requires a comparatively long time to print data on one paper sheet. In addition, it takes much time to develop the operating program of the printing module.